The effect of low light levels on postural stability in older adults with age-related macular degeneration.

Abstract

To investigate the effect of low light levels on postural stability in older adults with and without age-related macular degeneration (AMD). Participants included 28 older adults [14 with AMD (mean age ± S.D., 83.4±6.7years) and 14 controls with normal vision (74.6±3.3years)]. Postural stability was assessed with eyes open on both a firm and foam surface under four lighting conditions in a randomised order: photopic (~436lux, vertically at the eye), sudden reduction to mesopic (~436 to ~1lux), adapted mesopic (~1lux) and adapted mesopic with a light emitting diode (LED) door frame lighting system (~1.3lux), using the root mean square (RMS) of the centre of pressure measures derived from an electronic force plate in the anterior-posterior (AP) and medio-lateral (ML) directions. Visual function was assessed binocularly (visual acuity, contrast sensitivity and visual fields), physical function was assessed using standardised measures (sit-to-stand, grip strength and the timed walk test) and self-reported difficulties under low light levels were recorded using the Low Luminance Questionnaire. Data were analysed using linear mixed models. For all participants, low light levels significantly increased postural sway on the foam surface in the AP (p=0.01) but not ML (p=0.80) direction, but had no effect on postural stability on the firm surface. On the foam surface, while AP-RMS sway was significantly greater in the sudden (p<0.001) and adapted (p=0.02) mesopic compared to the photopic condition, sway for the adapted mesopic with the LED lighting system was not significantly different to the photopic condition (p=0.20). On the foam surface, AP-RMS (p=0.02) and ML-RMS (p<0.001) sway were significantly greater in the AMD compared to the control group. None of the measures of visual function was significantly associated with AP- or ML-RMS sway. On the foam surface, low light levels significantly reduced postural stability in older adults with and without AMD, and postural stability was significantly reduced for the AMD group compared to controls, regardless of light level. Importantly, the LED lighting system reduced sway under mesopic conditions, which was not significantly greater than that measured under photopic conditions in either group. These findings have important implications for enhancing the visual environment for older adults with and without AMD to improve postural stability and reduce the risk of falls in low lighting environments.